Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Sat Jul 17 2021

Valid 00Z Sun Jul 18 2021 - 00Z Sun Jul 25 2021

Today's guidance agrees on a brisk to strong trade pattern through
the period, with the majority of rainfall focused over
windward/mountain areas and lighter activity possibly straying
leeward at times.  Some differences exist for specifics of
moisture associated with eastern Pacific tropical systems though.

Expect central Pacific high pressure to strengthen over the coming
days, by early next week leading to further strengthening of
trades from already brisk levels.  Toward the end of the week the
high may retrograde enough to moderate the trades a bit but winds
should still be on the brisk side.  An upper low/inverted trough
and pocket of greater moisture will pass over the islands from
east to west during the weekend, possibly enhancing shower
activity somewhat.  A trailing upper ridge should favor lighter
rainfall early-mid week.  There is fair clustering toward the idea
of some moisture from Felicia reaching the southeastern islands
around Thursday and/or Friday, with the highest precipitable water
values tracking to the south of the state.  By Friday-Saturday the
00Z ECMWF becomes notably faster than the 00Z GFS and 00Z GEFS/12Z
ECMWF means with an area of potentially greater moisture from a
trailing system expected to form shortly.  Preference would be for
the majority scenario that has the axis of deep moisture reaching
only to 140-150W longitude by next Saturday.   

Rausch